Nitrogen-based chelates of transition metals such as Ti, Ni, Pd, Co and Fe have been actively investigated in recent years as olefin polymerization catalysts. Those incorporating bidentate α-diimine and tridentate bisminopyridine ligands have been found to be highly active catalysts for olefin polymerization.
More recently, similar investigations of coordination chemistry and catalysis have been extended to chromium (III) complexes containing certain imidizole-based chelate ligands. These complexes, when activated with methyl aluminoxane (“MAO”) were found to catalyze the oligomerization of ethylene. (See Ruther et al, Organometallics, 2001, 20, 1247-1250).
Despite the advances made in catalyst systems employing chromium, there is a continuing need for new catalysts that will provide a greater degree of control over polymerization processes. Homogenous, chromium-based catalysts are believed to possess the potential of providing better control over polymerization processes than many other organometallic catalysts. For example, a neutral nickel (II) catalyst containing bidentate monoanionic ligands produce linear α-olefins with a very wide range Schulz-Flory type distribution. An object of the present invention, therefore, is to provide novel chromium based catalysts useful in the polymerization of olefins.